Conjugated diene polymer, process for its production and rubber compositions containing the same

ABSTRACT

A process for producing a conjugated diene-based polymer which comprises, in the first modification, modifying a conjugated diene-based polymer having active chain ends, which is obtained by polymerizing a diene-based monomer singly or with other monomers and has a content of a cis-1,4 unit of 75% by mole or greater in the conjugated diene portion of the main chain, by reacting the active chain ends with a hydrocarbyloxysilane compound and reacting the modified polymer with a specific compound such as a hydrocarbyloxysilane compound, and a rubber composition containing the polymer modified in accordance with the above process and, preferably, 10 to 100 parts by weight of silica and/or carbon black per 100 parts by weight of the rubber component containing the modified polymer, are provided. The rubber composition containing silica and/or carbon black exhibits improved fracture properties, abrasion resistance, low heat buildup property and excellent workability. A process for producing a conjugated diene-based polymer exhibiting improved cold flow, a polymer produced in accordance with the process, and a rubber composition and a tire using the polymer are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of application Ser. No. 10/496,983, filed Nov. 5,2004 now U.S. Pat. No. 7,781,533, which claims benefit fromInternational Application No. PCT/JP02/12390, filed Nov. 27, 2002, whichclaims benefit from Japanese patent Application No. 2001-361354, filedon Nov. 27, 2001, the entire contents of each of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a conjugated diene-based polymer, aprocess for producing the polymer and a rubber composition using thepolymer. More particularly, the present invention relates to aconjugated diene-based polymer exhibiting improved low hysteresis lossproperty (low fuel consumption), enhanced reinforcement with fillers andsuppressed formation of gel, a process for producing the polymer and arubber composition and a pneumatic tire using the polymer.

BACKGROUND ART

Due to the social needs to save energy, recently, the decrease in thefuel consumption by automobiles is being extremely severely required. Asfor the properties of a tire, a further decrease in the rollingresistance is required in response to the requirement. As the method fordecreasing the rolling resistance of a tire, the use of a materialexhibiting smaller heat buildup as the rubber composition has beenwidely conducted although methods of optimizing the structure of thetire have also been studied.

To obtain a rubber composition exhibiting a small heat buildup,heretofore, many developments of technology on modifying rubber forrubber compositions using silica and carbon black as the filler havebeen conducted. In particular, the methods of modifying the interactionof fillers with active chain ends of diene-based polymers, which areobtained in accordance with the anionic polymerization usingorganolithium compounds, using alkoxysilane derivatives have beenproposed as the effective method.

Many of these methods are applied to polymers which are easily providedwith living active chain ends. However, rather few proposals are foundfor modification and improvement of cis-1,4-polybutadiene which isimportant, in particular, as the rubber for tire side walls and tiretreads. Moreover, the sufficient effect of the modification on rubbercompositions containing silica and carbon black has not always beenobtained. In particular, it is the actual situation that almost noeffect of the modification is obtained on the rubber compositionscontaining cis-1,4-polybutadiene and carbon black.

The conventional methods of the modification have a further problem inthat cold flow is the major obstacle for the actual application sincesufficient branching cannot be provided to the main chain and the effectof the modification inevitably decreases when partial coupling is madeto overcome this problem.

On the other hand, it has been attempted that a conjugated diene polymermodified with a silane is obtained by the reaction of an alkoxysilanecompound with active chain ends having a great cis-content which isobtained by using a rare earth catalyst. However, in accordance withthis method, the increase in the Mooney viscosity due to themodification with the silane is marked in many cases although a greateffect of improving the cold flow can be exhibited, and gel having avisible size is frequently formed in the separated copolymer.

Thus, improvements are required for this method from the standpoint ofworkability and properties.

DISCLOSURE OF THE INVENTION

Under the above circumstances, the present invention has an object ofproviding a process for producing a conjugated diene-based polymer whichsuppresses the formation of gel arising in the conventional processes,enhances the low hysteresis loss property and the reinforcing propertyand exhibits excellent abrasion resistance, mechanical properties andworkability when the polymer is used for rubber compositions andimproves cold flow, a polymer obtained in accordance with the process,and a rubber composition and a pneumatic tire using the polymer.

As the result of intensive studies by the present inventors to achievethe above object, it was found that bringing a hydrocarbyloxysilanecompound into reaction with a polymer having active chain ends, followedby conducting a secondary reaction with a specific compound was useful.It was also found that the undesirable formation of gel was closelyrelated to the change in catalyst residues during the heat treatment forremoval of a solvent or the like due to the presence of water or oxygen,and the problem could be remarkably improved in accordance with theprocess of modification of the present invention.

The present invention has been completed based on this knowledge.

The present invention provides:

-   (1) A process for producing a conjugated diene-based polymer which    comprises conducting a first modification of a conjugated    diene-based polymer having active chain ends, which is obtained by    polymerizing a diene-based monomer singly or in combination with    other monomers and has a content of a cis-1,4 unit of 75% by mole or    greater in a conjugated diene portion of a main chain, by bringing    the active chain ends into reaction with a hydrocarbyloxysilane    compound, and conducting a second modification of a polymer obtained    by the first modification by adding a hydrocarbyloxysilane compound    in a presence of a condensation accelerator;-   (2) A process for producing a conjugated diene-based polymer which    comprises conducting a first modification of a conjugated    diene-based polymer having active chain ends, which is obtained by    polymerizing a diene-based monomer singly or in combination with    other monomers and has a content of a cis-1,4 unit of 75% by mole or    greater in a conjugated diene portion of a main chain, by bringing    the active chain ends into reaction with a hydrocarbyloxysilane    compound, and bringing a polymer obtained by the first modification    into reaction with a partial ester of a polyhydric alcohol with a    carboxylic acid;-   (3) A process for producing a conjugated diene-based polymer which    comprises conducting a first modification of a conjugated    diene-based polymer having active chain ends, which is obtained by    polymerizing a diene-based monomer singly or in combination with    other monomers and has a content of a cis-1,4 unit of 75% by mole or    greater in a conjugated diene portion of a main chain, by bringing    the active chain ends into reaction with a hydrocarbyloxysilane    compound, adding a condensation accelerator, and conducting    condensation of a residue group of the hydrocarbyloxysilane compound    introduced at the active chain ends and the unreacted    hydrocarbyloxysilane compound;-   (4) A process for producing a conjugated diene-based polymer    described above in (1), which further comprises bringing a polymer    obtained by the second modification into reaction with a partial    ester of a polyhydric alcohol with a carboxylic acid;-   (5) A process for producing a conjugated diene-based polymer    described above in (3), which further comprises bringing a polymer    obtained by the condensation into reaction with a partial ester of a    polyhydric alcohol with a carboxylic acid;-   (6) A conjugated diene-based polymer which is produced in accordance    with a process described above in any one of (1) to (5);-   (7) A rubber composition which comprises a rubber component and    fillers, wherein the rubber component comprises the conjugated    diene-based polymer described above in (6); and-   (8) A pneumatic tire which comprises a rubber composition described    above in (7) in a rubber member constituting the tire.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

In the process of the present invention, a hydrocarbyloxysilane compoundis brought into reaction with active chain ends of a conjugateddiene-based polymer which has a content of a cis-1,4 unit of 75% by moleor greater and has the active chain ends, and, thereafter, the residuegroup of the hydrocarbyloxysilane compound introduced into the chainends is brought into reaction with a specific compound.

The process for producing the polymer which has a content of a cis-1,4unit of 75% by mole or greater and has the active chain ends is notparticularly limited. Any of the solution polymerization, the gas phasepolymerization and the bulk polymerization can be used, and the solutionpolymerization is preferable. The polymerization process may be any ofthe batch process and the continuous process.

Examples of the conjugated diene compound used as the monomer include1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene,2-phenyl-1,3-butadiene and 1,3-hexadiene. The conjugated diene compoundmay be used singly or in combination of two or more. Among thesecompounds, 1,3-butadiene is preferable.

Small amounts of other monomers may be present in combination with theabove conjugated diene monomer.

However, it is preferable that the conjugated diene monomer is presentin an amount of 80% by mole or more in the entire monomers.

The process for producing an intermediate of the conjugated diene-basedpolymer having 75% or greater of the cis-1,4 unit is not particularlylimited. It is preferable that a combination of at least one compoundselected from each of components shown in (A), (B) and (C) in thefollowing is used.

Component (A)

Compounds of rare earth elements selected from the following (A1) to(A4), which may be directly used as a solution in an inert organicsolvent or in a form supported with an inert solid.

(A1) Compounds of rare earth elements having an oxidation number of 3and having three ligands selected from carboxyl groups having 2 to 30carbon atoms, alkoxyl groups having 2 to 30 carbon atoms, aryloxy groupshaving 6 to 30 carbon atoms and α,γ-diketonyl groups having 5 to 30carbon atoms and complex compounds of these compounds with Lewis basecompounds which are selected from free carboxylic acids, free alcohols,α,γ-diketones, cyclic ethers, linear ethers, trihydrocarbylphosphinesand trihydrocarbyl phosphites.

Examples of compound (A1) include neodymium tri-2-ethylhexanoate, acomplex compound thereof with acetylacetone, neodymium trineodecanoate,a complex thereof with acetylacetone and neodymium tri-n-butoxide.

(A2) Complex compounds of trihalides of rare earth elements with Lewisacids. Examples include a THF complex of neodymium trichloride.

(A3) Organic compounds of rare earth elements having an oxidation numberof 3 in which at least one (substituted) allyl group is directly bondedto a rare earth atom. Examples include lithium salts oftetraallylneodymiums.

(A4) Organic compounds of rare earth elements having an oxidation numberof 2 or 3 and having at least one (substituted) cyclopentadienyl groupdirectly bonded to the rare earth atom and reaction products of theorganic rare earth compounds and trialkylaluminums or ionic compoundscomprising a non-coordinating anion and a counter cation.

Examples includedimethylaluminum-(μ-dimethyl)bis(pentamethylcyclopentadienyl)-samarium.

As the rare earth element in the above rare earth compounds, lanthanum,neodymium, praseodymium, samarium and gadolinium are preferable, andlanthanum, neodymium and samarium are more preferable.

Among the above compounds of component (A), neodymium salts ofcarboxylic acids and substituted cyclopentadienyl compounds of samariumare preferable.

Component (B)

At least one organoaluminum compound selected from the following (B1) to(B3). A plurality of compounds may be used in combination.

(B1) Trihydrocarbylaluminum compounds represented by the formula R¹²₃Al, wherein R¹² represents a hydrocarbon group having 1 to 30 carbonatoms and may represent the same group or different groups.

(B2) Hydrocarbylaluminum hydride represented by the formula R¹³ ₂AlH orR¹³AlH₂, wherein R¹³ represents a hydrocarbon group having 1 to 30carbon atoms, and a plurality of R¹³ may represent the same group ordifferent groups when the plurality of R¹³ are present.

(B3) Hydrocarbylaluminoxane compound having hydrocarbon groups having 1to 20 carbon atoms.

Examples of the compounds of component (B) include trialkylaluminums,dialkylaluminum hydrides, alkylaluminum dihydrides andalkylaluminoxanes. These compounds may be used as a mixture. Among thecompounds of (B), combinations of aluminoxanes and other organoaluminumcompounds are preferable.

Component (C)

A compound selected from the compounds shown in (C1) to (C4). However,component (C) is not essential when component (A) comprises a halogen ora non-coordinating anion or component (B) comprises an aluminoxane.

(C1) Inorganic and organic compounds of elements of Groups II, III andIV having hydrolyzable halogen atom and complex compounds thereof withLewis bases. Examples include alkylaluminum dihalides, dialkylaluminumhalides, silicon tetrachloride, tin tetrachloride, complexes of zincchloride with Lewis bases such as alcohols and complexes of magnesiumchloride with Lewis bases such as alcohols.

(C2) Organic halogen compounds having at least one structure selectedfrom tertiary alkyl halides, benzyl halides and allyl halides. Examplesinclude benzyl chloride, t-butyl chloride, benzyl bromide and t-butylbromide.

(C3) Zinc halides and complex compounds thereof with Lewis acids; and

(C4) Ionic compounds comprising a non-coordinating anion and a countercation. For example, triphenylcarboniumtetrakis-(pentafluorophenyl)borate is preferable.

For the preparation of the above catalyst, where necessary, the sameconjugated diene monomer as that used for the polymerization and/or anon-conjugated diene monomer may be preliminarily used in combinationwith components (A), (B) and (C) described above.

A portion or the entire amount of component (A) or (C) may be used inthe form supported on an inert support. In this case, the polymerizationcan be conducted in accordance with the so-called gas phasepolymerization.

The amount of the above catalyst can be suitably decided.

In general, the amount of component (A) is in the range of 0.001 to 0.5mmole per 100 g of the monomer. The ratio of the amount by mole ofcomponent (B) to the amount by mole of component (A) is in the range of5 to 1,000, and the ratio of the amount by mole of component (C) to theamount by mole of component (A) is in the range of 0.5 to 10.

The solvent used in the solution polymerization is an organic solventinert to the reaction, examples of which include hydrocarbon solventssuch as aliphatic, alicyclic and aromatic hydrocarbon compounds. Amongthe above compounds, compounds having 3 to 8 carbon atoms arepreferable.

Examples of the compound having 3 to 8 carbon atoms include propane,n-butane, isobutane, n-pentane isopentane, n-hexane, cyclohexane,propene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-pentene,2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene andethylbenzene. These solvents may be used singly or in combination of twoor more.

It is preferable that the temperature of the polymerization is selectedin the range of −80 to 150° C. and more preferably in the range of −20to 120° C. The polymerization may be conducted under the pressure formedby the reaction. However, in general, it is preferable that thepolymerization is conducted under a pressure sufficient for keeping themonomer substantially in the liquid state. The pressure depends on theindividual substances used for the polymerization, the medium of thepolymerization and the temperature of the polymerization. Where desired,a higher pressure may be applied. The higher pressure can be obtained inaccordance with a suitable method such as the application of thepressure to the reactor with a gas inert to the polymerization.

In the polymerization, it is preferable that the all materials takingpart in the polymerization such as the catalyst, the solvent and themonomer are used after substances adversely affecting the reaction suchas water, oxygen, carbon dioxide and protonic substances aresubstantially removed.

In the process of the present invention, it is preferable in thereaction of the first modification that at least 10% of the chain in theused polymer has the living property.

In the first modification, it is preferable that hydrocarbyloxysilanecompounds represented by general formula (I) and/or partial condensationproducts thereof are used as the hydrocarbyloxysilane compound which isused for the reaction with the active chain ends of the polymer. Generalformula (I) is:

wherein A¹ represents a monovalent group having at least one functionalgroup selected from (thio)epoxy group, (thio)isocyanate group,(thio)ketone group, (thio)aldehyde group, imine group, amide group,trihydrocarbyl ester group of isocyanuric acid, (thio)carboxylic acidester groups, alkali metal salts and alkaline earth metal salts of(thio)carboxylic acid ester groups, carboxylic acid anhydride groups,carboxylic acid halide groups and dihydrocarbyl ester groups of carbonicacid; R¹ represents a single bond or a divalent inert hydrocarbon group,R² and R³ each independently represent a monovalent aliphatichydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatichydrocarbon group having 6 to 18 carbon atoms; n represents an integerof 0 to 2; a plurality of OR³ may represent the same group or differentgroups when the plurality of OR³ are present; and no active protons oronium salts are present in a molecule.

In the above general formula (I), the imine group as the functionalgroup represented by A¹ includes ketimine groups, aldimine groups andamidine groups, and the (thio)carboxylic acid ester group as thefunctional group represented by A¹ includes unsaturated carboxylic acidester groups such as acrylates and methacrylates. Examples of the metalin the metal salt of (thio)carboxylic acid groups include alkali metals,alkaline earth metals, Al, Sn and Zn.

Examples of the divalent inert hydrocarbon group represented by R¹include alkylene groups having 1 to 20 carbon atoms. The alkylene groupmay be linear, branched or cyclic. Linear alkylene groups arepreferable. Examples of the linear alkylene group include methylenegroup, ethylene group, trimethylene group, tetramethylene group,pentamethylene group, hexamethylene group, octamethylene group,decamethylene group and dodecamethylene group.

Examples of the group represented by R² or R³ include alkyl groupshaving 1 to 20 carbon atoms, alkenyl groups having 2 to 18 carbon atoms,aryl groups having 6 to 18 carbon atoms and aralkyl groups having 7 to18 carbon atoms. The alkyl group and the alkenyl group may be linear,branched or cyclic. Examples of these groups include methyl group, ethylgroup, n-propyl group, isopropyl group, n-butyl group, isobutyl group,sec-butyl group, tert-butyl group, pentyl group, hexyl group, octylgroup, decyl group, dodecyl group, cyclopentyl group, cyclohexyl group,vinyl group, propenyl group, allyl group, hexenyl group, octenyl group,cyclopentenyl group and cyclohexenyl group.

The aryl group may have a substituent such as a lower alkyl group on thearomatic ring. Examples of the aryl group include phenyl group, tolylgroup, xylyl group and naphthyl group. The aralkyl group may have asubstituent such as a lower alkyl group on the aromatic ring. Examplesof the aralkyl group include benzyl group, phenetyl group andnaphthylmethyl group.

n represents an integer of 0 to 2 and preferably 0. It is necessary thatno active protons or onium salts are present in the molecule.

Examples of the hydrocarbyloxysilane compound having (thio)epoxy groupas the hydrocarbyloxysilane compound represented by general formula (I)include 2-glycidoxyethyltrimethoxysilane,2-glycidoxyethyltriethoxysilane,(2-glycidoxyethyl)methyldimethoxysilane,3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,(3-glycidoxypropyl)methyldimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltriethoxysilane,2-(3,4-epoxycyclohexyl)ethyl(methyl)dimethoxysilane and compoundsobtained by replacing epoxy group in the above compounds with thioepoxygroup. Among these compounds, 3-glycidoxypropyltrimethoxysilane and2-(3,4-epoxycyclohexyl)trimethoxysilane are preferable.

Examples of the hydrocarbyloxysilane compound having imine group includeN-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propane amine,N-(1-methylethylidene)-3-(triethoxysilyl)-1-propaneamine,N-ethylidene-3-(triethoxysilyl)-1-propaneamine,N-(1-methylpropylidene)-3-(triethoxysilyl)-1-propaneamine,N-(4-N,N-dimethylaminobenzylidene)-3-(triethoxysilyl)-1-propaneamine,N-(cyclohexylidene)-3-(triethoxysilyl)-1-propaneamine andtrimethoxysilyl compounds, methyldiethoxysilyl compounds,ethyldiethoxysilyl compounds, methyldimethoxysilyl compounds andethyldimethoxysilyl compounds corresponding to the above triethoxysilylcompounds. Among these compounds,N-(1-methylpropylidene)-3-(triethoxysilyl)-1-propaneamine andN-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propaneamine arepreferable.

Examples of other hydrocarbyloxy compounds include the followingcompounds. Examples of the compound having imine(amidine) group include1-[3-(triethoxysilyl)propyl]-4,5-dihydroimidazole,1-[3-(trimethoxysilyl)propyl]-4,5-dihydroimidazole and3-[10-(triethoxysilyl)decyl]-4-oxazoline. Among these compounds,3-(1-hexamethyleneimino)propyl(triethoxy)silane,(1-hexamethyleneimino)methyl(trimethoxy)silane,1-[-3-(triethoxysilyl)propyl]-4,5-dihydroimidazole and1-[3-(trimethoxysilyl)propyl]-4,5-dihydroimidazole are preferable.Further examples includeN-(3-triethoxysilylpropyl)-4,5-dihydroimidazole,N-(3-isopropoxysilylpropyl)-4,5-dihydroimidazole andN-(3-methyldiethoxysilylpropyl)-4,5-dihydroimidazole. Among thesecompounds, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole ispreferable.

Examples of the compound having a carboxylic acid ester group include3-methacryloyloxypropyltriethoxysilane,3-methacryloyloxypropyltrimethoxysilane,3-methacryloyloxypropylmethyldiethoxysilane and3-methacryloyloxypropyltriisopropoxysilane. Among these compounds,3-methacryloyloxypropyltrimethoxysilane is preferable. Examples of thecompound having isocyanate group include3-isocyanatopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane,3-isocyanatopropylmethyldiethoxysilane and3-isocyanatopropyltriisopropoxysilane. Among these compounds,3-isocyanatopropyltriethoxysilane is preferable. Examples of thecarboxylic acid anhydride include 3-triethoxysilylpropylsuccinicanhydride, 3-trimethoxysilylpropylsuccinic anhydride and3-methyldiethoxysilylpropylsuccinic anhydride. Among these compounds,3-triethoxysilylpropylsuccinic anhydride is preferable.

The hydrocarbyloxysilane compound may be used singly or in combinationof two or more. Partial condensation products of the abovehydrocarbyloxysilane compounds may also be used.

In the above first modification, the chain ends of the polymer havingthe active ends and the hydrocarbyloxysilane compound are first broughtinto the reaction. It is necessary that the introduced residue group isthen treated in accordance with one of the processes of (1) the reactionwith a partial ester of a polyhydric alcohol with a carboxylic acid forstabilization or (2) the reaction with the residual or freshly addedhydrocarbyloxysilane compound in the presence of a condensationaccelerator. As the latter process (2), one of the following processes(2-1) to (2-3) can be conducted:

(2-1) After the first modification, the fresh hydrocarbyl-oxysilanecompound and a condensation accelerator is added, and the secondmodification is conducted;

(2-2) After the first modification, a condensation accelerator is added,and the condensation of the residual group of hydrocarbyl-oxysilanecompound introduced into the chain ends and the unreactedhydrocarbyloxysilane is conducted; and

(2-3) After the reaction described above in (2-1) or (2-2), the reactionwith a partial ester of a polyhydric alcohol with a carboxylic acid isconducted for stabilization.

The partial ester of a polyhydric alcohol with a carboxylic acid is apartial ester which is an ester of a polyhydric alcohol with acarboxylic acid and has at least one hydroxyl group. Specifically,esters of sugars or modified sugars having 4 or more carbon atoms andfatty acids are preferable. More preferable examples of the esterinclude (a) partial esters of polyhydric alcohols with fatty acids andstill more preferably partial esters of polyhydric alcohols withsaturated or unsaturated higher fatty acids having 10 to 20 carbon atomswhich may be monoesters, diesters or triesters and (b) ester compoundsobtained by bonding 1 to 3 molecules of partial esters of polybasiccarboxylic acids and higher alcohols to polyhydric alcohols.

As the polyhydric alcohol used as the material for the above partialester, sugars having at least 3 hydroxyl groups and 5 or 6 carbon atomswhich may be hydrogenated or not hydrogenated, glycols and polyhydroxylcompounds are preferable. As the fatty acid used as the material,saturated or unsaturated fatty acids having 10 to 20 carbon atoms suchas stearic acid, lauric acid and palmitic acid are preferable.

Among the partial esters of polyhydric alcohols with fatty acids, estersof fatty acids with sorbitan are preferable. Specific examples of thepartial ester include sorbitan monolaurate, sorbitan monopalmitate,sorbitan monostearate, sorbitan tristearate, sorbitan monooleate andsorbitan trioleate.

Examples of the commercial products include SPAN 60 (sorbitan stearate),SPAN 80 (sorbitan monooleate) and SPAN 85 (sorbitan trioleate), whichare trade names by ICI Company.

It is preferable that the amount of the partial ester is in the range of0.2 to 10 moles and more preferably in the range of 1 to 10 moles per 1mole of the hydrocarbyloxysilyl group provided to the polymer.

As the hydrocarbyloxysilane compound described above, ahydrocarbyloxysilane compound represented by general formula (II) and/ora partial condensation product thereof may be used in combination withthe hydrocarbyloxysilane compound represented by general formula (I)and/or the partial condensation product thereof. General formula (II)is:

wherein A² represents a monovalent group having at least one functionalgroup selected from cyclic tertiary amine groups, acyclic tertiary aminegroups, pyridine groups, sulfide groups, polysulfide groups and nitrilegroups; R⁴ represents a single bond or a divalent inert hydrocarbongroup, R⁵ and R⁶ each independently represent a monovalent aliphatichydrocarbon group having 1 to 20 carbon atoms or a monovalent aromaticgroup having 6 to 18 carbon atoms; m represents an integer of 0 to 2; aplurality of OR⁶ may represent the same group or different groups whenthe plurality of OR⁶ are present; and no active protons or onium saltsare present in a molecule.

The partial condensation product is a compound having the bond SiOSiformed by the condensation of a portion of (but not the entire amountof) SiOR of the hydrocarbyloxysilane compound.

The hydrocarbyloxysilane compound represented by general formula (II)and/or the partial condensation product thereof does not directly reactwith the active chain ends substantially and remains in the reactionsystem as the unreacted substance. Therefore, the compound and/or thecondensation product is consumed by the condensation with the residuegroup of the hydrocarbyloxysilane compound introduced into the activechain ends.

The acyclic tertiary amine represented by A² in general formula (II)shown above can include N,N-(disubstituted) aromatic amines such asN,N-(disubstituted) anilines. The cyclic tertiary amine can have(thio)ethers as a portion of the ring. The divalent inert hydrocarbongroup represented by R⁴ and the groups represented by R⁵ or R⁶ are thesame as those represented by R¹, R² and R³, respectively, in generalformula (I). It is necessary that no active protons or onium salts arepresent in a molecule.

Examples of the hydrocarbyloxysilane compound having the acyclictertiary amine group as the hydrocarbyloxysilane compound represented bygeneral formula (II) include 3-dimethylaminopropyl(triethoxy)silane,3-dimethylaminopropyl(trimethoxy)silane,3-diethylaminopropyl(triethoxy)silane,3-diethylaminopropyl(trimethoxy)silane,2-dimethylaminoethyl(triethoxy)silane,2-dimethylaminoethyl(trimethoxy)silane,3-dimethylaminopropyl(diethoxy)methylsilane and3-dibutylaminopropyl(triethoxy)silane. Among these compounds,3-diethylaminopropyl(triethoxy)silane and3-dimethylaminopropyl(triethoxy)silane are preferable.

Examples of the hydrocarbyloxysilane compound having the cyclic tertiaryamine group include 3-(1-hexamethyleneimino)propyl(triethoxy)silane,3-(1-hexamethyleneimino)propyl(trimethoxy)silane,(1-hexamethyleneimino)methyl(trimethoxy)silane,(1-hexamethyleneimino)methyl(triethoxy)silane,2-(1-hexamethyleneimino)ethyl(triethoxy)silane,2-(1-hexamethyleneimino)ethyl(trimethoxy)silane,3-(1-pyrrolidinyl)propyl(triethoxy)silane,3-(1-pyrrolidinyl)propyl(trimethoxy)silane,3-(1-heptamethyleneimino)propyl(triethoxy)silane,3-(1-dodecamethyleneimino)propyl(triethoxy)silane,3-(1-hexamethyleneimino)propyl(diethoxy)methylsilane and3-(1-hexamethyleneimino)propyl(diethoxy)ethylsilane. Among thesecompounds, 3-(1-hexamethyleneimino)propyl(triethoxy)silane ispreferable.

Examples of the other hydrocarbyloxysilane compound include2-(trimethoxysilylethyl)pyridine, 2-(triethoxysilylethyl)pyridine and4-ethylpyridine.

The hydrocarbyloxysilane compound may be used singly or in combinationof two or more. Partial condensation products of thesehydrocarbyloxysilane compounds can also be used.

In process (2-1) described above, as hydrocarbyloxysilane compound IIwhich is condensed with the residue group of hydrocarbyloxysilanecompound I introduced into the active chain ends of the polymer, atleast one compound selected from hydrocarbyloxysilane compoundsrepresented by general formula (I), partial condensation productsthereof, hydrocarbyloxysilane compounds represented by general formula(II), partial condensation products thereof, hydrocarbyloxysilanecompounds represented by general formula (III) and partial condensationproducts thereof can be used. General formula (III) is:

wherein A³ represents a monovalent group having at least one functionalgroup selected from alcohol groups, thiol groups, primary amine groups,onium salts thereof, cyclic secondary amine groups, onium salts thereof,acyclic amine groups, onium salts thereof, onium salts of cyclictertiary amine groups, onium salts of acyclic tertiary amine groups,groups having allyl group or benzyl-Sn bond, sulfonyl group, sulfinylgroup and nitrile group; R⁷ represents a single bond or a divalent inerthydrocarbon group, R⁸ and R⁹ each independently represent a monovalentaliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalentaromatic group having 6 to 18 carbon atoms; q represents an integer of 0to 2; a plurality of OR⁹ may represent the same group or differentgroups when the plurality of OR⁹ are present.

In general formula (III) shown above, the primary amine represented byA³ includes aromatic amines such as aniline, and the acyclic secondaryamine represented by A³ includes N-(monosubstituted) aromatic aminessuch as N-(monosubstituted) anilines. The onium salt of an acyclictertiary amine represented by A³ includes onium salts ofN,N-(disubstituted) aromatic amines such as N,N-(disubstituted)anilines. The cyclic secondary amine and the cyclic tertiary amine mayhave (thio)ether as a portion of the ring. The divalent inerthydrocarbon group represented by R⁷ and groups represented by R⁸ and R⁹are the same as those represented by R¹, R² and R³, respectively, ingeneral formula (I) shown above.

Examples of the hydrocarbyloxysilane compound represented by generalformula (III) include 3-aminopropyltrimethoxysilane,3-aminopropyltriethoxysilane, hydroxymethyltrimethoxysilane,hydroxymethyltriethoxysilane, mercaptomethyltrimethoxysilane,mercaptomethyltriethoxysilane, aminophenyltrimethoxysilane,aminophenyltriethoxysilane, 3-(N-methylamino)propyltrimethoxysilane,3-(N-methylamino)propyltriethoxysilane,octadecyldimethyl(3-trimethylsilylpropyl)ammonium chloride,octadecyldimethyl(3-triethylsilylpropyl)ammonium chloride,cyanomethyltrimethoxysilane, cyanomethyltriethoxysilane,sulfonylmethyltrimethoxysilane, sulfonylmethyltriethoxysilane,sulfinylmethyltrimethoxysilane and sulfinylmethyltriethoxysilane.

Hydrocarbyloxysilane compound II may be used singly or in combination oftwo or more.

In the present invention, for process (2) described above whichcomprises the reaction with the residual or freshly addedhydrocarbyloxysilane compound in the presence of a condensationaccelerator, the polymer having the active chain ends andhydrocarbyloxysilane I added to the reaction system in a substantiallystoichiometric amount are first brought into the reaction with eachother, and hydrocarbyloxysilyl group is introduced into thesubstantially entire chain ends (the first modification). A compoundhaving hydrocarbyloxyl group is brought into reaction with thehydrocarbyloxysilyl group introduced above, and the residue group ofhydrocarbyloxysilane compound in an amount more than the equivalentamount is introduced in the active chain ends. Therefore, a greatereffect on the low heat buildup property and the workability can beexhibited, and process (2) described above is preferable to process (1)described above.

In the present invention, when the hydrocarbyloxysilane compound is analkoxysilyl compound, it is preferable that the condensation between thealkoxysilyl groups in process (2) described above takes place betweenthe free alkoxysilane (residual or freshly added) and the alkoxysilylgroup at the chain ends, and, in some cases, between the alkoxysilylgroups at the chain ends. The reaction between the free alkoxysilanes isnot necessary. Therefore, when the alkoxysilane compound is freshlyadded, it is preferable from the standpoint of the efficiency that thereactivity of hydrolysis of the freshly added alkoxysilane compound isnot greater than the reactivity of hydrolysis of the alkoxysilyl groupat the chain ends. For example, a combination such that a compoundhaving trimethoxysilyl group having a great reactivity of hydrolysis isused as alkoxysilane I and, as the freshly added alkoxysilane II, acompound having an alkoxysilyl group having a smaller reactivity ofhydrolysis than alkoxysilane II such as triethoxysilyl group is used, ispreferable. In contrast, for example, a combination such that a compoundhaving triethoxysilyl group is used as alkoxysilane I and a compoundhaving trimethoxysilyl group is used as alkoxysilane II is notpreferable from the standpoint of the efficiency of the reactionalthough this combination is included in the present invention.

For the modification in the present invention, any of the solutionpolymerization and the solid phase polymerization can be used. Thesolution polymerization is preferable and may be conducted in a solutioncontaining the unreacted monomer used in the polymerization. The form ofthe polymerization is not particularly limited, and the batch reactionusing a batch reactor may be conducted, or the continuous reaction usinga multi-stage reactor or a inline mixer may be conducted. It isimportant that the modification is conducted after the polymerizationhas been completed and before the treatment for removal of the solvent,the treatment with water, the treatment by heating and treatmentsnecessary for separation of the polymer are conducted.

The temperature of the modification can be held at the temperature ofthe polymerization of the conjugated diene-based polymer. Specifically,a temperature in the range of 20 to 100° C. is preferable. When thetemperature is lowered, viscosity of the polymer tends to increase. Whenthe temperature is elevated, the active chain ends tend to bedeactivated. Therefore, a temperature outside the above range is notpreferable.

To accelerate the second modification described above, it is preferablethat the modification is conducted in the presence of a condensationaccelerator. As the condensation accelerator, a combination of metalcompounds widely known as the curing catalyst for the room temperaturevulcanizable (RTV) silicone of the alkoxy condensation curing type andwater can be used. For example, the combination of a salt of tin with acarboxylic acid and/or a titanium alkoxide and water is preferable. Theprocess for adding water used in the condensation accelerator into thereaction system is not particularly limited. A solution in an organicsolvent compatible with water such as an alcohol may be used. Water mayalso be directly injected, dispersed or dissolved into a hydrocarbonsolvent using one of various chemical engineering processes.

It is preferable that the condensation accelerator described above is acombination of at least one metal compound selected from metal compoundsdescribed in (1) to (3) in the following and water.

(1) Salts of tin having an oxidation number of 2 with carboxylic acidshaving 3 to 30 carbon atoms represented by the following generalformula:Sn(OCOR¹⁰)₂wherein R¹⁰ represents an organic group having 2 to 19 carbon atoms, anda plurality of R¹⁰ may represent the same group or different groups whenthe plurality of R¹⁰ are present.

(2) Compounds of tin having an oxidation number of 4 and represented bythe following general formula:R¹¹ _(r)SnA⁴ _(t)B¹ _((4−t−r))wherein r represents an integer of 1 to 3, t represents an integer of 1or 2 and t+r represents an integer of 3 or 4; R¹¹ represents analiphatic hydrocarbon group having 1 to 30 carbon atoms; B¹ representshydroxyl group or a halogen atom; and A⁴ represents a group selectedfrom (a) carboxyl groups having 2 to 30 carbon atoms, (b) α,γ-dionylgroups having 5 to 30 carbon atoms, (c) hydrocarbyloxyl groups having 3to 30 carbon atoms and (d) siloxyl groups having three substituentswhich are selected from hydrocarbyl groups having 1 to 20 carbon atomsand hydrocarbyloxyl groups having 1 to 20 carbon atoms, and the threesubstituents may be same with or different from each other, and aplurality of A⁴ may represent the same group or different groups whenthe plurality of A⁴ are present.

(3) Compounds of titanium having an oxidation number of 4 andrepresented by the following general formula:A⁵ _(x)TiB² _((4−x))wherein x represents an integer of 2 or 4; A⁵ represents (a) ahydrocarbyloxyl group having 3 to 30 carbon atoms or (b) a siloxyl grouphaving three substituents which are selected from alkyl groups having 1to 30 carbon atoms and hydrocarbyloxyl groups having 1 to 20 carbonatoms, and a plurality of A⁵ may represent the same group or differentgroups when the plurality of A⁵ are present; and B² represents anα,γ-dionyl group having 5 to 30 carbon atoms.

As the salt of tin with a carboxylic acid described above, specifically,(1) salts of divalent tin with dicarboxylic acids (which is preferablysalts of carboxylic acids having 8 to 20 carbon atoms) and (2) salts oftetravalent dihydrocarbyltin with dicarboxylic acids [including salts ofbis(hydrocarbyldicarboxylic acids)], bis(α,γ-diketonates)alkoxy halides,monocarboxylic acid salt hydroxides, alkoxy(trihydrocarbylsiloxides),alkoxy(dihydrocarbylalkoxysiloxides), bis(trihydrocarbylsiloxides) andbis(dihydrocarbylalkoxysiloxides, are preferable. As the hydrocarbylgroup directly bonded to the tin atom, hydrocarbyl groups having 4 ormore carbon atoms are preferable, and hydrocarbyl groups having 4 to 8carbon atoms are more preferable.

Examples of the titanium compound described above includetetraalkoxides, dialkoxybis(α,γ-diketonates) andtetrakis(trihydrocarbyloxysiloxides) of titanium having an oxidationnumber of 4, and tetraalkoxides are preferable. As water, water itselfor water in the form of a solution, for example, in an alcohol, or inthe form of micelles dispersed in a hydrocarbon solvent can be used.Where necessary, water latently contained in a compound which candischarge water in the reaction system such as water adsorbed on thesurface of a solid or water in a hydrate can also be effectively used.

These two components constituting the condensation accelerator may beadded to the reaction system separately or as a mixture preparedimmediately before the reaction. It is not preferable that the mixtureis kept for a long time since the metal compound is decomposed.

As for the amount of the condensation accelerator, it is preferable thatthe ratios of the amount by mole of the metal in the metal compounddescribed above and the amount by mole of water effective for thereaction to the amount by mole of the entire hydrocarbyloxysilyl grouppresent in the reaction system are both 0.1 or greater. It is preferablethat water effective for the reaction is present in an amount such thatthe ratio of the amount by mole of the effective water to the amount bymole of the entire hydrocarbyloxysilyl group bonded to the chain ends ofthe polymer before the condensation is in the range of about 0.5 to 3although the upper limit is different depending on the object and thecondition of the reaction. It is preferable that the ratio of the amountby mole of the metal in the metal compound described above to the amountby mole of water effective for the reaction described above is in therange of 1/0.5 to 1/20 although the preferable ratio is differentdepending on the condition of the reaction.

In the present invention, after the hydrocarbyloxysilane compound isbrought into reaction with the active chain ends of the polymer and thenreaction is allowed to proceed by addition of the condensationaccelerator, the ester of a polyhydric alcohol with a carboxylic aciddescribed above may be brought into a further reaction.

In the present invention, where desired, conventional antioxidants andshort stop agents may be added during the modification after the residuegroup of the hydrocarbyloxysilane compound has been introduced into theactive chain ends of the polymer.

After the above modifications, conventional post treatments areconducted, and the modified polymer of the object substance can beobtained. The analysis of the groups at the chain ends of the modifiedpolymer can be conducted in accordance with the chromatography using aliquid as the carrier such as the high performance liquid chromatography(HPLC) and the thin layer chromatography and the nuclear magneticresonance spectroscopy (NMR).

It is preferable that the Mooney viscosity (ML₁₊₄, 100° C.) of themodified polymer is in the range of 10 to 150 and more preferably in therange of 15 to 70. When the Mooney viscosity decreases, the physicalproperties such as the fracture properties tend to decrease. When theMooney viscosity increases, the workability becomes poor, and the mixingwith compounding ingredients becomes difficult.

The present invention also provides the modified polymer obtained asdescribed above.

When the modified polymer of the present invention is used as a rubbercomponent in a rubber composition containing inorganic compounds such assilica and carbon black as the fillers, the interaction with the filleris enhanced for any types of the filler. Thus, the fracture properties,the abrasion resistance and the low heat buildup property can beimproved simultaneously, and the excellent workability can be exhibited.

It is preferable that the rubber composition of the present inventioncomprises the modified polymer described above at least in an amount of30% by weight. When the amount is less than 30% by weight, it isdifficult that the rubber composition exhibiting the desired propertiesis obtained, and the object of the present invention is not achieved,occasionally. It is more preferable that the modified polymer iscomprised in an amount of 35% by weight or greater and most preferablyin an amount in the range of 40 to 100% by weight.

The modified polymer may be used singly or in combination of two ormore. Other rubber components such natural rubber and diene-basedsynthetic rubbers may be used in combination with the modified polymer.Examples of the diene-based synthetic rubber include styrene-butadienecopolymers (SBR), polybutadiene (BR), polyisoprene (IR), butyl rubber(IIR), ethylene-propylene copolymers and mixtures of these rubbers. Therubber may have a portion having a branched structure formed by using apolyfunctional modifier such as tin tetrachloride and silicontetrachloride.

It is preferable that the rubber composition of the present inventioncomprises fillers. As the filler, any filler can be used as long as thefiller can be used for conventional rubber compositions. Examples of thefiller include carbon black and inorganic fillers. Among these fillers,carbon black, silica and alumina are preferable.

Carbon black is not particularly limited. For example, SRF, GPF, FEF,HAF, ISAF and SAF can be used. Carbon black having an iodine adsorption(IA) of 60 mg/g or greater and a dibutyl phthalate absorption (DBP) of80 ml/100 g or greater is preferable. The effect of improving thegripping property and the fracture properties is increased by usingcarbon black. HAF, ISAF and SAF providing excellent abrasion resistanceare more preferable.

Silica is not particularly limited. Examples of silica include wetsilica (hydrated silicic acid), dry silica (anhydrated silicic acid),calcium silicate and aluminum silicate. Among these types of silica, thewet silica which most remarkably exhibits the effect of improving thefracture properties and simultaneously improving the wet grippingproperty and the low rolling resistance is more preferable.

As alumina, alumina represented by the following general formula (IV) ispreferable:Al₂O₃ .nH₂O  (IV)wherein n represents a number of 1 to 3.

As the other inorganic filler, substances represented by the followinggeneral formula (V) are preferable:mM₁ .xSiO_(y) .zH₂O  (V)wherein M₁ represents at least one substance selected from metalsselected from the group consisting of aluminum, magnesium, titanium andcalcium, oxides and hydroxides of these metals and hydrates of thesesubstances, and m, x, y and z represent integers of 1 to 5, 0 to 10, 2to 5 and 0 to 10, respectively.

Metals such as potassium, sodium, iron and magnesium and elements suchas fluorine may be further comprised.

Examples of the inorganic filler include silica, hydrate of alumina(Al₂O₃.H₂O), aluminum hydroxide [Al(OH)₃] such as gibbsite and bayerite,magnesium hydroxide (MgO), magnesium oxide (MgO), talc (3MgO.4SiO₂.H₂O),attapulgite (5MgO.8SiO₂.9H₂O), titanium white (TiO₂), titanium black(TiO_(2n−1)), calcium oxide (CaO), calcium hydroxide [Ca(OH)₂], aluminummagnesium oxide (MgO.Al₂O₃), clay (Al₂O₃.2SiO₂), kaolin(Al₂O₃.2SiO₂.2H₂O), pyrophillite (Al₂O₃.4SiO₂.H₂O), bentonite(Al₂O₃.4SiO₂.2H₂O), aluminum silicate (Al₂SiO₅, Al₄.3SiO₄.5H₂O and thelike), magnesium silicate (Mg₂SiO₄, MgSiO₃ and the like), calciumsilicate (Ca₂.SiO₄ and the like), aluminum calcium silicate(Al₂O₃.CaO.2SiO₂ and the like), magnesium calcium silicate (CaMgSiO₄),hydrogen which adjusts the charge such as various types of zeolite,feldspar and mica. In general formula (V) representing the inorganicfiller, it is preferable that M¹ represents aluminum.

It is preferable that the inorganic filler has a diameter of 10 μm orsmaller and more preferably 3 μm or smaller. When the diameter of theinorganic filler is 10 μm or smaller, the fracture properties and theabrasion resistance of the vulcanized rubber composition can be keptexcellent.

In the present invention, the inorganic filler may be used singly or incombination of two or more. The filler is used in an amount in the rangeof 10 to 250 parts by weight per 100 parts by weight of the rubbercomponent. From the standpoint of the reinforcing property and theeffect thereof to improve various physical properties, it is preferablethat the amount is in the range of 10 to 100 parts by weight. When theamount is less than the above range, the effect of improving thefracture properties is not sufficient. When the amount exceeds the aboverange, the workability tends to be poor.

The rubber composition of the present invention comprises the modifiedpolymer obtained in accordance with the process described above. Ingeneral, a composition comprising a rubber component comprising at least30% by weight of the modified polymer and 10 to 100 parts by weight ofsilica and/or carbon black per 100 parts by weight of the rubbercomponent is used.

When silica is used as the reinforcing filler in the rubber compositionof the present invention, a silane coupling agent can be added so thatthe reinforcing property of silica is further enhanced. Examples of thesilane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(2-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-trimethoxysilylpropylbenzothiazolyl tetrasulfide,3-triethoxysilylpropylbenzolyl tetrasulfide, 3-triethoxysilylpropylmethacrylate monosulfide, 3-trimethoxysilylpropoyl methacrylatemonosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide,3-mercaptopropyldimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide anddimethoxymethylsilylpropylbenzothiazolyl tetrasulfide. Among thesecompounds, bis(3-triethoxysilylpropyl)polysulfides and3-trimethoxysilylbenzothiazyl tetrasulfide are preferable from thestandpoint of the effect of improving the reinforcing property. Thesilane coupling agent may be used singly or in combination of two ormore.

In the rubber composition of the present invention, since the modifiedpolymer having the functional group exhibiting a great affinity withsilica and introduced into the chain ends is used, the amount of thesilane coupling agent can be decreased from that in conventional rubbercompositions. In general, the silane coupling agent is used in an amountin the range of 1 to 20% by weight although the preferable amount isdifferent depending on the type of the silane coupling agent. When theamount of the silane coupling agent is less than the above range, it isdifficult that the effect as the coupling agent is sufficientlyexhibited. When the amount exceeds the above range, there is thepossibility that gelation of the rubber component takes place. From thestandpoint of the effect as the coupling agent and the prevention of theformation of gel, it is preferable that the amount of the silanecoupling agent is in the range of 5 to 15% by weight.

Where necessary, the rubber composition of the present invention maycomprise various chemicals conventionally used in the rubber industrysuch as vulcanizing agents, vulcanization accelerators, process oils,antioxidants, scorch inhibitors, zinc oxide and stearic acid as long asthe object of the present invention is not adversely affected.

The rubber composition of the present invention can be obtained bymixing the components using a mixer, for example, an open mixer such asrolls or a closed mixer such as a Banbury mixer. The rubber compositioncan be vulcanized after forming and applied to various rubber products.For example, the composition can be applied to tire members such as tiretreads, under-treads, carcasses, side walls and beads and otherindustrial rubber products such as vibration isolation rubbers, dockfenders, belts and hoses. The composition is particularly advantageouslyapplied to rubber for tire treads.

The pneumatic tire of the present invention using the rubber compositiondescribed above can exhibit excellent durability due to the enhancedreinforcing property with the filler while the low fuel consumption issurely maintained. Examples of the gas filling the tire include the airand inert gases such as nitrogen.

EXAMPLES

The present invention will be described more specifically with referenceto examples in the following. However, the present invention is notlimited to the examples.

The properties of the polymer were evaluated in accordance with thefollowing methods.

<<Physical Properties of a Polymer>>

The microstructure of the butadiene portion of a polymer was obtained inaccordance with the infrared spectroscopy (the Morero's method).

The Mooney viscosity of a polymer was measured at 100° C. using a testerof the RLM-01 type manufactured by TOYO SEIKI SEISAKUSHO Co., Ltd.

To find whether macrogel was present or absent, a 0.2 w/v % solution ofa polymer was prepared using tetrahydrofuran as the solvent, and thepresence or the absence of macrogel was examined by visual observationafter the solution was left standing at the room temperature withoutbeing stirred for 24 hours.

<<Mooney Viscosity of a Rubber Composition>>

The Mooney viscosity [ML₁₊₄/130° C.] was measured at 130° C. inaccordance with the method of Japanese Industrial Standard K6300-1994.

<<Physical Properties of a Vulcanized Rubber>>

(1) Low Heat Buildup Property

Using an apparatus for measuring viscoelasticity (manufactured byRHEOMETRICS Company), tan δ (50° C.) was measured at a temperature of50° C., a strain of 5% and a frequency of 15 Hz. The smaller the valueof tan δ, the smaller the heat buildup.

(2) Fracture Property (Tensile Strength)

The strength at break (T_(b)) was measured by a tensile tester inaccordance with the method of Japanese Industrial Standard K6301-1995.

(3) Abrasion Resistance

The amount of abrasion was measured at the room temperature under aslipping ratio of 60% using a Lambourn abrasion tester. The result isexpressed as an index of the abrasion resistance using the abrasionresistance of the control as the reference which is set at 100. Thegreater the index, the better the abrasion resistance.

<Preparation of a Catalyst>

Into a glass bottle having a volume of 100 ml and fitted with a rubbercap, which had been dried and purged with nitrogen, 7.11 g of acyclohexane solution (15.2% by weight) of butadiene, 0.59 ml of acyclohexane solution (0.56 M) of neodymium decanoate, 10.32 ml of atoluene solution (3.23 M as the concentration of aluminum) ofmethylaluminoxane MAO (manufactured by TOSO AKZO Co., Ltd; PMAO) and7.77 ml of a hexane solution (0.90 M) of diisobutylaluminum hydride(manufactured by KANTO KAGAKU Co., Ltd.) were placed successively inthis order, and the resultant mixture was aged at the room temperaturefor 2 minutes. Then, 1.45 ml of a hexane solution (0.95 M) ofdiethylaluminum chloride (manufactured by KANTO KAGAKU Co., Ltd.) wasadded, and the resultant mixture was aged at the room temperature for 15minutes under intermittent stirring. The concentration of neodymium inthe catalyst solution thus obtained was 0.011 M (mole/liter).

Preparation Examples 1 to 4 Polymers E to H

<Preparation of a Polymer Intermediate>

Into a glass bottle having a volume of about 900 ml and fitted with arubber cap, which had been dried and purged with nitrogen, a cyclohexanesolution of dried and purified butadiene and dry cyclohexane were placedso that the glass bottle contained 400 g of a cyclohexane solutioncontaining 12.5% by weight of butadiene. Then, 2.28 ml of the catalystsolution prepared above (containing 0.025 mmole of neodymium) was added,and the polymerization was conducted in a water bath at 50° C. for 1.0hour.

<First Modification>

A silane compound of the type shown in Table 1 was added as a hexanesolution (1.0 M) in an amount shown in Table 1 as the agent for thefirst modification, and the resultant mixture was treated at 50° C. for60 minutes.

<Treatments after the First Modification>

To the mixture obtained above, 1.2 ml of an ester of a polyhydricalcohol with a carboxylic acid (manufactured by KANTO KAGAKU Co., Ltd.)shown in Table 1 was added, and the modification was conducted at 50° C.for 1 hour. The reaction was terminated by adding 2 ml of a 5%isopropanol solution of an antioxidant2,2′-methylenebis(4-ethyl-6-t-butylphenol) (NS-5) to the polymerizationsystem, and a polymer was obtained after reprecipitation withisopropanol containing a small amount of NS-5 and drying using a drum.Polymers E to H were obtained in this manner. The results of theanalysis of the obtained polymers are shown in Table 1.

Preparation Example 5 to 7 and 12 Polymers I to K and P

After the polymerization of 1,3-butadiene was completed in accordancewith the same procedures as those conducted in Preparation Example 1,the modification was conducted as described in the following.

<First Modification>

A silane compound of the type shown in Table 1 was added as a hexanesolution (1.0 M) in an amount shown in Table 1 as the agent for thefirst modification, and the first modification was conducted by treatingthe resultant mixture at 50° C. for 60 minutes.

<Treatments after the First Modification>

To the mixture obtained above, 1.76 ml (corresponding to 70.5 eq/Nd) ofa cyclohexane solution (1.01 M) of tin bis(2-ethylhexanoate) as theagent for condensation accelerator and 32 μl (corresponding to 70.5eq/Nd) of ion-exchanged water were added, and the resultant mixture wastreated in a water bath at 50° C. for 1.0 hour. Thereafter, the sameprocedures as those conducted in Preparation Example 1 were conducted.Polymers I to K and P were obtained in this manner. The results of theanalysis of the obtained polymers are shown in Table 1.

Preparation Example 8 to 11 Polymers L to O

After the polymerization of 1,3-butadiene was completed in accordancewith the same procedures as those conducted in Preparation Example 1,the modification was conducted as described in the following.

<First Modification>

A silane compound of the type shown in Table 1 was added as a hexanesolution (1.0 M) in an amount shown in Table 1 as the agent for thefirst modification, and the reaction of the first stage was conducted bytreating the resultant mixture at 50° C. for 30 minutes.

<Treatments after the First Modification>

To the mixture obtained above, a silane compound of the type shown inTable 1 (the agent for the second modification) was added as a hexanesolution (1.0 M) in an amount shown in Table 1, and the resultantmixture was stirred at 50° C. for 30 minutes. Then, 1.76 ml(corresponding to 70.5 eq/Nd) of a cyclohexane solution of tinbis(2-ethylhexanoate) as the agent for condensation accelerator and 32μl (corresponding to 70.55 eq/Nd) of ion-exchanged water were added, andthe resultant mixture was treated in a water bath at 50° C. for 1 hour.Thereafter, the same procedures as those conducted in PreparationExample 1 were conducted. Polymers L to O were obtained in this manner.The results of the analysis of the obtained polymers are shown in Table1.

Preparation Example 13 Polymer Q

Polymer Q was obtained in accordance with the same procedures as thoseconducted in Preparation Example 8 except that titaniumtetrakis(2-ethylhexyloxide) was used in place of tinbis(2-ethylhexanoate). The results of the analysis of the obtainedpolymer are shown in Table 1.

Comparative Preparation Example 1 Polymer a without Modification

Polymer A was obtained in accordance with the same procedures as thoseconducted in Preparation Example 1 except that 1.83 ml of the catalystsolution was added, none of the first modification and the secondmodification was conducted after the polymer intermediate was prepared,and the reaction was terminated by adding 2 ml of a 5% isopropanolsolution of an antioxidant (NS-5). The microstructure of the obtainedpolymer was as follows: the content of the cis-unit: 95.5%; the contentof the trans-unit: 3.9; and the content of the vinyl unit: 0.6%. Theresults of the analysis of the obtained polymers are shown in Table 1.

Comparative Preparation Examples 2 to 4 Polymers B to D with SingleStage Modification

Polymers B to D were obtained in accordance with the same procedures asthose conducted in Preparation Example 1 except that the firstmodification alone was conducted and the second modification was notconducted. The results of the analysis of the obtained polymers areshown in Table 1.

TABLE 1 Comparative Preparation Example Preparation Example 1 2 3 4Polymer (in Preparation A B C D Example or Comparative PreparationExample) mode of modification none first alone first alone first aloneAgent for the first modification (hydrocarbyl- oxysilane compound) type— GPMOS TEOSIPDI GPMOS + TEOSIPDI amount * 0 (23.5) (23.5) (23.5 + 23.5)Agent for the second modification (added after the first modification)(hydrocarbyloxysilane compound) type — — — — amount * — — — —Condensation accelerator — — — — Partial ester of — — — — polyhydricalcohol with carboxylic acid Evaluation macrogel none great great greatamount amount amount Mooney viscosity 37 92 45 42 (ML₁₊₄, 100° C.)Comparative Preparation Example Preparation Example 1 2 3 4 Polymer (inPreparation E F G H Example or Comparative Preparation Example) mode ofmodification (1) (1) (1) (1) Agent for the first modification(hydrocarbyl- oxysilane compound) type GPMOS TEOSIPDI GPMOS + GPMOSTEOSIPDI amount * (23.5) (23.5) (23.5 + 23.5) (23.5) Agent for thesecond modification (added after the first modification)(hydrocarbyloxysilane compound) type — — — — amount * — — — —Condensation accelerator — — — — Partial ester of STO STO STO SMLpolyhydric alcohol with carboxylic acid Evaluation macrogel none nonenone none Mooney viscosity 59 45 36 56 (ML₁₊₄, 100° C.) PreparationComparative Example Preparation Example 5 6 7 Polymer (in Preparation IJ K Example or Comparative Preparation Example) mode of modification(2-2) (2-2) (2-2) Agent for the first modification (hydrocarbyl-oxysilane compound) type GPMOS TEOSIPDI GPMOS + TEOSIPDI amount * (23.5)(23.5) (23.5 + 23.5) Agent for the second modification (added after thefirst modification) (hydrocarbyloxysilane compound) type — — — amount *— — — Condensation accelerator BEHAS/H₂O BEHAS/H₂O BEHAS/H₂O Partialester of — — — polyhydric alcohol with carboxylic acid Evaluationmacrogel none none none Mooney viscosity 93 54 53 (ML₁₊₄, 100° C.)Preparation Comparative Example Preparation Example 8 9 10 11 Polymer(in Preparation L M N O Example or Comparative Preparation Example) modeof modification (2-1) (2-1) (2-1) (2-1) Agent for the first modification(hydrocarbyl- oxysilane compound) type GPMOS TEOSIPDI GPMOS GPMOSamount * (23.5) (23.5) (23.5) (23.5) Agent for the second modification(added after the first modification) (hydrocarbyloxysilane compound)type TEOSIPDI GPMOS APTEOS MAPTEOS amount * (23.5) (23.5) (23.5) (23.5)Condensation BEHAS/H₂O BEHAS/H₂O BEHAS/H₂O BEHAS/H₂O accelerator Partialester of — — — — polyhydric alcohol with carboxylic acid Evaluationmacrogel none none none none Mooney viscosity 54 51 66 58 (ML₁₊₄, 100°C.) Preparation Comparative Example Preparation Example 12 13 Polymer(in Preparation P Q Example or Comparative Preparation Example) mode ofmodification (2-2) (2-1) Agent for the first modification (hydrocarbyl-oxysilane compound) type GPMOS + GPMOS DMAPTEOS amount * (23.5 + 23.5)(23.5) Agent for the second modification (added after the firstmodification) (hydrocarbyloxysilane compound) type — TEOSIPDI amount * —(23.5) Condensation BEHAS/H₂O TEHO/H₂O accelerator Partial ester ofpolyhydric alcohol with carboxylic acid Evaluation — — macrogel nonenone Mooney viscosity 53 89 (ML₁₊₄, 100° C.) Notes * The number in theparenthesis shows the amount of the added hydrocarbyloxysilane compound(mole equivalent based on the amount of neodymium) GPMOS:3-Glycidoxypropyltrimethoxysilane (epoxy) TEOSIPDLN-(3-Triethoxysilylpropyl)-4,5-dihydroimidazole (amidine (imine))DMAPTEOS: 3-Dimethylaminopropyl(triethoxy)silane (imine) STO: Sorbitantrioleate (sugar ester) SML: Sorbitan monolaurate (sugar ester) APTEOS:3-Aminopropyltriethoxysilane (primary amine) MAPTEOS:3-(N-Methylamino)propyltriethoxysilane (secondary amine) BEHAS: Tinbis(2-ethyl hexanoate) TEHO: Titanium tetrakis(2-ethylhexyloxide)

Examples 1 to 13 and Comparative Example 1 to 4

Using polymers A to Q obtained above, rubber compositions containingsilica (Formulation 1) and rubber compositions containing carbon black(Formulation 2) were prepared. Formulations 1 and 2 are shown in Table2.

TABLE 2 Components of formulation (part by weight) Formulation 1Formulation 2 First stage polymer obtained in 70 70 Preparation Examplenatural rubber 30 30 carbon black 0 50 silica 55 0 aromatic oil 10 10stearic acid 2 2 coupling agent 5.5 0 antioxidant 6C 1 1 Second stageZnO 3 3 vulcanization 1 0.5 accelerator DPG vulcanization 1 0.5accelerator DM vulcanization 1 0.5 accelerator sulfur 1.5 1.5 Silica:Manufactured by Nippon Silica Kogyo Co., Ltd.; the trade name: NIPSIL AQCarbon black: Manufactured by TOKAI CARBON Co., Ltd.; the trade name:SIEST KH (N339) Coupling agent: Manufactured by DEGUSSA Company; asilane coupling agent; the trade name: Si69; bis(3-triethoxysilylpropyl)tetrasulfide 6C: N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine DPG:Diphenylguanidine DM: Mercaptobenzothiazyl disulfide NS:N-t-Butyl-2-benzothiazylsulfenamide

The Mooney viscosity (130° C.) of the above rubber compositions beforethe vulcanization was measured. The rubber compositions were vulcanizedin the condition of 160° C. for 15 minutes, and the low heat buildupproperty, the fracture property (the tensile strength) and the abrasionresistance of the vulcanized rubber were evaluated. The results of theevaluation are shown in Table 3.

TABLE 3 Comparative Example Example 1 2 3 4 1 2 3 4 Polymer A B C D E FG H Formulation 1 (rubber composition containing silica) Mooneyviscosity 70 104 68 77 89 65 75 84 (ML₁₊₄, 130° C.) tensile strength21.0 20.0 19.3 19.6 20.2 19.7 19.7 19.1 Tb (MPa) low heat buildup 0.1410.106 0.116 0.095 0.090 0.117 0.136 0.085 tan δ (10%, 50° C.) abrasionresistance 100 103 107 106 110 108 111 111 (index) Formulation 2 (rubbercomposition containing carbon black) Mooney viscosity 60 — 63 — — 59 —61 (ML₁₊₄, 100° C.) tensile strength 21.8 — 20.2 — — 20.9 — — Tb (MPa)low heat buildup 0.160 — 0.145 — — 0.134 — — tan δ (10%, 50° C.)abrasion resistance 100 — 104 — — 109 — 111 (index) Comparative ExampleExample 5 6 7 8 9 10 11 12 13 Polymer I J K L M N O P Q Formulation 1(rubber composition containing silica) Mooney viscosity 104 77 86 88 8194 91 88 97 (ML₁₊₄, 130° C.) tensile strength 19.5 19.6 18.4 19.6 18.620.1 19.6 19.7 19.0 Tb (MPa) low heat buildup 0.079 0.092 0.073 0.0710.082 0.070 0.072 0.085 0.088 tan δ (10%, 50° C.) abrasion resistance111 110 109 110 109 114 113 111 108 (index) Formulation 2 (rubbercomposition containing carbon black) Mooney viscosity — 64 — 69 — 72 6966 72 (ML₁₊₄, 100° C.) tensile strength — 21.2 — 21.6 — 22.1 21.9 21.521.3 Tb (MPa) low heat buildup — 0.117 — 0.104 — 0.099 0.109 0.118 0.110tan δ (10%, 50° C.) abrasion resistance — 111 — 115 — 119 114 110 113(index)

The results in Table 1 show that the polymers prepared in accordancewith the conventional process having the first modification alone(polymers B to D) contained a great amount of macrogel and, in contrast,the polymers prepared in accordance with the process of the presentinvention (polymers E to Q) contained no macrogel. The results in Table3 show that the rubber compositions using the modified polymers of thepresent invention (Examples 1 to 13) suppressed the increase in theMooney viscosity and remarkably improved the low heat buildup propertyand the abrasion resistance without adverse effects on the fractureproperty (the tensile strength) in both cases of the silica-basedformulation and the carbon black-based formulation.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, since the problem of macrogelformed in the finishing step of a polymer after the removal of thesolvent and the drying can be overcome, an excessive increase in theMooney viscosity of the polymer is suppressed, and the workability ofthe rubber composition in the unvulcanized condition can be remarkablyimproved. In both cases of the silica-based formulation and the carbonblack-based formulation, the interaction with silica or carbon black canbe enhanced, and the fracture property, the abrasion resistance and thelow heat buildup property of the vulcanized rubber can be simultaneouslyimproved. Therefore, the polymer can be applied to rubber compositionsfor tires. Moreover, the resistance to cold flow of the diene-basedpolymer can be improved.

The invention claimed is:
 1. A process for producing a conjugateddiene-based polymer which comprises conducting a first modification of aconjugated diene-based polymer having active chain ends, which isobtained by polymerizing a diene-based monomer singly or in combinationwith other monomers and has a content of a cis-1,4 unit of 75% by moleor greater in a conjugated diene portion of a main chain, by bringingthe active chain ends into reaction with a hydrocarbyloxysilanecompound, and conducting a second modification of a polymer obtained bythe first modification by adding a hydrocarbyloxysilane compound in apresence of a condensation accelerator, wherein at least one ofhydrocarbyloxysilane compounds represented by general formula (I) andpartial condensation products thereof is used as thehydrocarbyloxysilane compound in the first modification, general formula(I) being:

wherein A¹ represents a monovalent group having at least one functionalgroup selected from (thio)epoxy group, (thio)isocyanate group,(thio)ketone group, (thio)aldehyde group, imine group, amide group,trihydrocarbyl ester group of isocyanuric acid, (thio)carboxylic acidester groups, alkali metal salts and alkaline earth metal salts of(thio)carboxylic acid ester groups, carboxylic acid anhydride groups,carboxylic acid halide groups and dihydrocarbyl ester groups of carbonicacid; R¹ represents a single bond or a divalent inert hydrocarbon group,R² and R³ each independently represent a monovalent aliphatichydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatichydrocarbon group having 6 to 18 carbon atoms; n represents an integerof 0 to 2; a plurality of OR³ may represent a same group or differentgroups when the plurality of OR³ are present; and no active protons oronium salts are present in a molecule, and wherein, after the firstmodification is conducted by bringing the active chain ends intoreaction with the hydrocarbyloxysilane compound represented by generalformula (I) (hydrocarbyloxysilane compound I), at least one compound(hydrocarbyloxysilane compound II) selected from hydrocarbyloxysilanecompounds represented by general formula (II) and/or partialcondensation products thereof and hydrocarbyloxysilane compoundsrepresented by general formula (III) and/or partial condensationproducts thereof and a condensation accelerator are added and broughtinto reaction with the polymer obtained by the first modification,general formula (II) being:

wherein A² represents a monovalent group having at least one functionalgroup selected from cyclic tertiary amine groups, acyclic tertiary aminegroups, pyridine groups, sulfide groups, polysulfide groups and nitrilegroups; R⁴ represents a single bond or a divalent inert hydrocarbongroup, R⁵ and R⁶ each independently represent a monovalent aliphatichydrocarbon group having 1 to 20 carbon atoms or a monovalent aromaticgroup having 6 to 18 carbon atoms; m represents an integer of 0 to 2; aplurality of OR⁶ may represent a same group or different groups when theplurality of OR⁶ are present; and no active protons or onium salts arepresent in a molecule, and general formula (III) being:

wherein A³ represents a monovalent group having at least one functionalgroup selected from alcohol groups, thiol groups, primary amine groups,onium salts thereof, cyclic secondary amine groups, onium salts thereof,acyclic amine groups, onium salts thereof, onium salts of cyclictertiary amine groups, onium salts of acyclic tertiary amine groups,groups having allyl group or benzyl-Sn bond, sulfonyl group, sulfinylgroup and nitrile group; R⁷ represents a single bond or a divalent inerthydrocarbon group, R⁸ and R⁹ each independently represent a monovalentaliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalentaromatic group having 6 to 18 carbon atoms; q represents an integer of 0to 2; a plurality of OR⁹ may represent a same group or different groupswhen the plurality of OR⁹ are present.
 2. A process for producing aconjugated diene-based polymer according to claim 1, wherein thecondensation accelerator comprises at least one compound selected from agroup consisting of metal compounds shown in (1) to (3) and water, (1)to (3) being: (1) Salts of tin having an oxidation number of 2 withcarboxylic acids having 3 to 30 carbon atoms represented by a followinggeneral formula:Sn(OCOR¹⁰⁾ ₂ wherein R¹⁰ represents an organic group having 2 to 19carbon atoms, and a plurality of R¹⁰ may represent a same group ordifferent groups when the plurality of R¹⁰ are present; (2) Compounds oftin having an oxidation number of 4 and represented by a followinggeneral formula:R¹¹ _(r)SnA⁴ _(t)B¹ _((4−t−r)) wherein r represents an integer of 1 to3, t represents an integer of 1 or 2 and t+r represents an integer of 3or 4; R¹¹ represents an aliphatic hydrocarbon group having 1 to 30carbon atoms; B¹ represents hydroxyl group or a halogen atom; and A⁴represents a group selected from (a) carboxyl groups having 2 to 30carbon atoms, (b) α,γ-dionyl groups having 5 to 30 carbon atoms, (c)hydrocarbyloxyl groups having 3 to 30 carbon atoms and (d) siloxylgroups having three substituents which are selected from hydrocarbylgroups having 1 to 20 carbon atoms and hydrocarbyloxyl groups having 1to 20 carbon atoms, the three substituents being same with or differentfrom each other, and a plurality of A⁴ may represent a same group ordifferent groups when the plurality of A⁴ are present; and (3) Compoundsof titanium having an oxidation number of 4 and represented by afollowing general formula:A⁵ _(x)TiB² _((4−x)) wherein x represents an integer of 2 or 4; A⁵represents (a) a hydrocarbyloxyl group having 3 to 30 carbon atoms or(b) a siloxyl group having three substituents which are selected fromalkyl groups having 1 to 30 carbon atoms and hydrocarbyloxyl groupshaving 1 to 20 carbon atoms, and a plurality of A⁵ may represent a samegroup or different groups when the plurality of A⁵ are present; and B²represents an α,γ-dionyl group having 5 to 30 carbon atoms.
 3. A processfor producing a conjugated diene-based polymer according to claim 1,wherein a polymerization catalyst used for the polymerization to obtainthe conjugated diene-based polymer having active chain ends comprises acombination of at least one compound selected from each of elementsshown in (A), (B) and (C): (A) Rare earth compounds selected fromfollowing (A1) to (A4), which may be directly used as a solution in aninert organic solvent or in a form supported with an inert solid, (A1)Compounds of rare earth elements having an oxidation number of 3 andhaving three ligands selected from carboxyl groups having 2 to 30 carbonatoms, alkoxyl groups having 2 to 30 carbon atoms, aryloxy groups having6 to 30 carbon atoms and α,γ-diketonyl groups having 5 to 30 carbonatoms and complex compounds of these compounds with Lewis basecompounds; (A2) Complex compounds of trihalides of rare earth elementswith Lewis acids; (A3) Organic compounds of rare earth elements havingan oxidation number of 3 in which at least one (substituted) allyl groupis directly bonded to a rare earth atom; and (A4) Organic compounds ofrare earth elements having an oxidation number of 2 or 3 and having atleast one (substituted) cyclopentadienyl group directly bonded to a rareearth atom and reaction products of the organic rare earth compounds andtrialkylaluminums or ionic compounds comprising a non-coordinating anionand a counter cation; (B) Organoaluminum compounds selected fromcompounds shown in (B1) to (B3): (B1) Trihydrocarbylaluminum compoundsrepresented by a formula R¹² ₃Al, wherein R¹² represents a hydrocarbongroup having 1 to 30 carbon atoms and may represent a same group ordifferent groups; (B2) Hydrocarbylaluminum hydride represented by aformula R¹³ ₂AlH or R¹³AlH₂, wherein R¹³ represents a hydrocarbon grouphaving 1 to 30 carbon atoms, and a plurality of R¹³ may represent a samegroup or different groups when the plurality of R¹³ are present; and(B3) Hydrocarbylaluminoxane compound having hydrocarbon groups having 1to 20 carbon atoms; and (C) Compounds selected from compounds shown in(C1) to (C4): (C1) Inorganic and organic compounds of elements of GroupsII, III and IV having at least one hydrolyzable halogen atom and complexcompounds thereof with Lewis bases; (C2) Organic halogen compoundshaving at least one structure selected from tertiary alkyl halides,benzyl halides and allyl halides; (C3) Zinc halides and complexcompounds thereof with Lewis acids; and (C4) Ionic compounds comprisinga non-coordinating anion and a counter cation; the element shown in (C)being not essential when element (A) comprises a halogen or anon-coordinating anion or element (B) comprises an aluminoxane.
 4. Aprocess for producing a conjugated diene-based polymer according toclaim 3, wherein the rare earth element is at least one element selectedfrom a group consisting of lanthanum, neodymium, praseodymium, samariumand gadolinium.
 5. A process for producing a conjugated diene-basedpolymer according to claim 1, wherein the conjugated diene-based polymeris at least one polymer selected from the group consisting ofpolybutadiene, polyisoprene and copolymers of butadiene with otherconjugated dienes.